Glass composition



,QJUNITED STATES PATENT OFFICE,

GLASS COIWPO SITION Walter Hanlein, Berlin- Haselhorst, and HermannKrefft, Berlin-Friedrichshagen, Germany, assignors to General ElectricCompany, a corporation of New York No Drawing. Original application June27, 1936,

Serial No. 87,770. Divided and this application January 25, 1937, Serialmany July 12, 1935 1 Claim.

The present invention relates to electric gaseous discharge devicesgenerally, and more particularly to vapor relatively high intensiti aredevices which operate at A particular object of the invention is toprovide a glass of novel composition for use in the arts generally, andwhich is especially adapted to use within a high intensity gaseousdischarge lamp. Another object of the invention is to provide a novelglass whi ch will resist blackening when used as a lamp envelope of ahigh intensity lamp in which the radiations of caesium are added tothose of mercury advantages of the the following detailed s Still otherobjects and invention will appear from pecification.

The invention consists in a new and novel composition of matter, ashereinafter set forth and claimed.

It has been proposed to modify the light emitted by high intensitymercury vapor arc lamps by admixing caesium with the mercury, and bythen increasing the temperature of the discharge vessel so as to achievea sufiiciently high caesium vapor pressure so that the caesium radiationconstitutes a considerable portion of the total'radiation from thedischarge. For this purpose it has been found necessary t temperaturesof the order of 500 operate these lamps at C. or more. At

such high temperatures it has been found that there is appreciableblackening of the lamp envelope where any of the usual glasses of theprior able blackening provide d a novel glass of our invention is usedfor the lamp envelope. This novel glass has a silica content amountingto of the silica and the amount to more than 50% only 25 a boric oxidecontent of 10 to 20%, an alumina content of 25 to 35% oxide content of20 to 40%.

and an earth alkali Furthermore the sum boric oxide should not of theentire composition. We have found that high intensity mercury vaporlamps having envelopes consisting of such a glass are not only subjectedto no blackening during operation but are also resistant to reduction bythe caesium operating temperatures.

vapor even at the high Calcium oxide and bari- No. 122,310. 'In Gerumoxide are preferably used as the earth alkali oxides in this glass, butwhere desired they are partially replaced by magnesium oxide and zincoxide.

The proportion of caesium added to the mercury is ordinarily of theorder of 0.2 to but in some cases, as where the lamp is operated at anespecially high temperature, the caesium is introduced in proportions ashigh at 12%, in which case the caesium radiation becomes especiallystrong in relation to the mercury radiation. It has been found that evenwith the larger of these caesium additions, and with the correspondinglyhigher temperature of the discharge vessel which is necessary therewith,no blackening of the lamp envelope occurs either as a result of thedischarge itself or as a result of the chemical influence of the caesiumvapor.

This novel glass of our invention has a low coeflicient of expansion,and at the same time has a high softening temperature, in excess of thatrequired by the operating temperatures of the mercury-caesium lamp.

The novel glass composition which we have discovered resists blackeningwhen subjected to a high temperature mercury-caesium discharge contains25 to 40% silica, to 20% boric oxide, 25 to 35% alumina and 20 to 40%earth alkali oxide, the sum of the silica and the boric oxide in allcases being less than 50%. Such a glass has a low coefi'icient ofexpansion and is likewise resistant to chemical attack by either mercuryvapor or caesium vapor, even at temperatures considerably in excess of500 C., so that no blackening of the envelope is produced by thesevapors during operation of the lamps. A glass of the followingcomposition has proved to be especially This glass has a softeningtemperature considerably in excess of that required by any of theselamps, so that a discharge at several atmospheres pressure can beoperated in a lamp constructed thereof without damage.

have used to illustrate our invention without de-W V parting from thespirit thereof.

2,1a5,eea p p is This is a division of our co-pending applica- 7 tion,Serial No. 87,770, filed June 27, 1 936.

What we claim as new and desire to secure by 7 Letters Patent of theUnited States, is:-

1. A glass having the following composition: Per cent SiOz- B201 10A1203 30 C210 1 15 Ba0 10 WALTER HANLEIN.

HERMANN KREFFT.

